Builder systems are key elements in detergent compositions. Indeed, they allow to counteract the deleterious effects of multivalent ions of the water, soils or fibers on the washing process. The prior art on builder systems is very crowded since detergent manufacturers have constantly been trying to improve the performance of the builder systems in their products, and have proposed sophisticated builder systems. This effort has been even more important in the field of liquid heavy duty detergents, so as to match the performance of granular detergent compositions.
Because of environmental issues, detergent manufacturers are constantly trying to formulate detergent compositions which contain environmentally compatible ingredients and have outstanding performance. It is well known that citric acid may act as a builder in detergents, and citric acid enjoys a well-established safety pedigree. It is therefore desirable to formulate an aqueous liquid detergent composition comprising citric acid as a builder.
It is also well known that citric acid has a rather poor building performance compared to other builders; in other terms, in order to obtain an acceptable building performance in a given detergent composition containing citric acid as a builder, one will have to incorporate important amounts of citric acid. However, high levels of citric acid in an aqueous liquid detergent will inevitably lead to physical stability problems, in that such a detergent will split in two phases, one of which contains essentially water and the most of the citric acid, the other comprising water and the most of the surfactant. This problem is even more acute in detergent compositions containing high amounts of surfactants.
Without specifically addressing this stability problem, compositions containing citric acid and which are said to be stable are disclosed for instance in EP 0 237 075, US 4 532 067, DE 2 203 004. The problem is more specifically addressed in DE 3 544 236, GB 2 140 819 or GB 2 140 818. The above references all recommend the introduction in the compositions of solvents or hydrotropes.
US 4,780,234 provides an alternative in that it discloses liquid detergent compositions comprising builders including citric acid, wherein the phase stability problem is solved by using a specific alkyl glycoside surfactant.
It has now been found that an alternative to the above solutions could be found in that a stable aqueous liquid detergent composition containing a major amount of citric acid can be formulated by incorporating therein a minor amount of an alk(en)yl substituted succinic acid, which is an auxiliary builder compound; this specific compound has already been described as a builder in the art; indeed, EP 0 212 723 and GB 2 197 340 disclose liquid detergent compositions comprising both citric acid and an alk(en)yl substituted succinic acid. However, these compositions are opposite to the compositions of the present invention in that they contain only a minor amount of citric acid, and the major constituent of the builder system is the substituted succinic acid.